This invention relates to control valves used to variably control fluid flow.
The prior art discloses a number of "hard-trim" control valves, wherein a variable closure is effected between a rigid central member and a rigid annular or cylindrical member. Typical devices are disclosed in Shaw, U.S. Pat. No. 263,731 (1882); Haley, U.S. Pat. No. 654,891 (1900); Johnson, U.S. Pat. No. 1,030,890 (1912); Slattery, U.S. Pat. No. 1,477,722 (1923); and Larner, U.S. Pat. No. 1,514,975 (1921). In these devices, closure was effected in one of two ways. In devices such as shown in Haley '891 or Slattery '722, a slideable cylindrical sleeve, in sealed engagement with the housing of the valve, served as the moveable valve element which could seat against the stationary central member. In devices such as Shaw '731, Johnson '890, or Larner '975, the central member, or a portion of it, was slideable such that it could effect a variable closure with, or seat against, a circular seat which was attached to, or part of, the valve housing.
While these "hard trim" designs were capable of metal-to-metal closure, there were drawbacks to this type of design. As the valve element approached the seat element, and the distances between the two elements became small, instability due to the lower pressures caused by the rapidly moving fluid flowing through the small passageway resulted in slamming and bounce-back of the valve.
There disadvantages were recognized, and attempts were made to use a deformable resilient member to effect variable closure in the valve. Welker, U.S. Pat. No. 2,917,269 (1959), discloses a control valve in which the deformation of a centrally disposed plug of resilient material is used to effect a variable closure. However, the design of Welker '269 proved to be unsatisfactory because the resilient plug was easily damaged by the destructive shearing stresses established by the compression of the resilient plug, the flow through the passageway, and the pressure differential across the valve. These shearing stresses tended to cause cutting or fatigue of the resilient plug, and would cause the resilient plug to separate from the backing members or abutment spiders. This damage to the plug could result in valve failure or poor valve performance.
Sachnik, U.S. Pat. No. 3,368,787 (1968); Culpepper, U.S. Pat. No. 3,380,470 (1968); and Welker, U.S. Pat. No. 3,746,300 (1973), all recognized these problems, and attempted, through various artifices, to extend the life of the resilient plug. None of these designs contemplated a means whereby the valve could be closed with a metal-to-metal seal, either in the event of plug damage or otherwise.
Boynton, U.S. Pat. No. 2,429,546 (1943), and Griffin, U.S. Pat. No. 3,342,215 (1967), contemplated the use of a cylindrical plug of resilient material with a passage through it to control fluid flow. By placing the plug in axial compression, the size of the passageway could be varied. However, in both of these designs, the plug was relatively long compared with its diameter. Furthermore, in Griffin '215, the slip/stick frictional forces associated with the operation of a valve of that design could cause valve "hunting" and overshoot. Neither design was capable of effecting a metal-to-metal seal, and neither design utilized a rigid seat member.
Accordingly, an object of the present invention is to provide a control valve which reduces or eliminates the slamming and bounce-back and consequent valve chatter associated with the "hard trim" type control valves.
Another object of the invention is to provide a control valve utilizing a resilient valve closure element in which the resilient element is less subject to cutting and fatigue and consequent failure.
Another object of the invention is to provide a control valve whose operating characteristic may be altered by relatively simple design changes.
Yet a further object of this invention is to provide a control valve which uses a resilient valve closure element having a wide seal area capable of sealing over entrapped foreign particles and yet which is also capable of a metal-to-metal type seal.
Other objects and purposes of this invention will appear from the following descriptions, examples, and claims.